JP2619048B2 - Electron optical device for obtaining quasi-parallel minute electron beam - Google Patents
Electron optical device for obtaining quasi-parallel minute electron beamInfo
- Publication number
- JP2619048B2 JP2619048B2 JP1037138A JP3713889A JP2619048B2 JP 2619048 B2 JP2619048 B2 JP 2619048B2 JP 1037138 A JP1037138 A JP 1037138A JP 3713889 A JP3713889 A JP 3713889A JP 2619048 B2 JP2619048 B2 JP 2619048B2
- Authority
- JP
- Japan
- Prior art keywords
- electron beam
- objective lens
- lens
- electron
- diameter
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
- 238000010894 electron beam technology Methods 0.000 title claims description 48
- 230000003287 optical effect Effects 0.000 title claims description 11
- 239000000523 sample Substances 0.000 description 19
- 230000004075 alteration Effects 0.000 description 6
- 238000002003 electron diffraction Methods 0.000 description 3
- 238000000034 method Methods 0.000 description 3
- 230000004907 flux Effects 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 230000008094 contradictory effect Effects 0.000 description 1
- 238000002050 diffraction method Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 238000012916 structural analysis Methods 0.000 description 1
- 230000003313 weakening effect Effects 0.000 description 1
Description
【発明の詳細な説明】 （産業上の利用分野） 本発明は反射電子回折装置等の電子線を用いた試料の
微小領域観察装置に用いられる微小径平行電子線ビーム
を得るための電子光学装置に関する。Description: BACKGROUND OF THE INVENTION (Industrial application field) The present invention relates to an electron optical device for obtaining a small-diameter parallel electron beam used in a device for observing a small region of a sample using an electron beam such as a reflection electron diffraction device. About.
（従来の技術） 電子線を用いる試料観察装置として走査型電子顕微鏡
とか電子回折装置が用いられている。走査型電子顕微鏡
は電子ビームをきわめて小さな径に絞るため、電子線束
の開き角がかなり大きなものである。このため走査型電
子顕微鏡の映像は高い分解能が得られるが、電子ビーム
の開きが大きいため、試料面に形成された微小径の深い
穴とか細い溝例えば半導体ウエハ上に形成された数ミク
ロン程度の溝の立体構造を観察したいような場合電子線
が穴とか溝の側面に当って、穴とか溝の底を観察できな
いと云う問題がある。また電子回折装置は通常mmオーダ
のビーム径の電子線を用い、試料面のmmオーダの径の領
域の平均的構造を分析するのに用いられており、試料面
のミクロンオーダの微小領域の結晶の大きさとか方位等
を測定するためにはビーム径をミクロン以下に絞り、か
つ平行に近い電子線束が必要となる。(Prior Art) A scanning electron microscope or an electron diffraction device is used as a sample observation device using an electron beam. Since the scanning electron microscope narrows the electron beam to an extremely small diameter, the opening angle of the electron beam is considerably large. For this reason, the image of the scanning electron microscope can obtain high resolution, but since the aperture of the electron beam is large, a deep hole with a small diameter or a narrow groove formed on the sample surface, for example, a few microns formed on a semiconductor wafer, When observing the three-dimensional structure of the groove, there is a problem that the electron beam hits the side of the hole or the groove and the bottom of the hole or the groove cannot be observed. Electron diffractometers are usually used to analyze the average structure of a sample surface in the order of mm in diameter using an electron beam with a beam diameter in the order of mm. In order to measure the size, direction, etc., the beam diameter needs to be reduced to a micron or less and an electron beam that is nearly parallel is required.
（発明が解決しようとする課題） 走査型電子顕微鏡で試料面の微細でかつ深い凹凸の底
部まで明瞭に観察できるようにするには、開き角の小さ
な、かつ絞り径も小さな電子線プローブを形成する必要
があり、また電子線回折法でも、微小領域の構造解析を
行うためには開き角の充分小さな微小径電子ビームを得
る必要がある。しかしビーム径を小さく絞ると云うこと
と、平行に近い細い線束を得ると云うことは互いに相反
する要求であって、両者を同時に満足させ得る電子光学
系を得ることは甚だ困難である。困難の理由は、微小径
の平行に近い線束を得るためにはレンズから長い距離を
隔てた点を収束点として細い電子線束を収束させること
になるが、この場合、レンズ光軸から離れた電子線がレ
ンズ光軸と交わる点はレンズのわづかな収差によっても
所定のビーム収束点から大きくずれるため、電子線束を
レンズの近くに収束させる（収束角大）場合よりレンズ
収差の影響が強く現われるようになるからである。(Problems to be Solved by the Invention) In order to clearly observe the fine and deep irregularities on the sample surface with a scanning electron microscope, an electron beam probe with a small opening angle and a small aperture diameter is formed. It is also necessary to obtain a small-diameter electron beam having a sufficiently small opening angle in order to perform a structural analysis of a minute region by the electron beam diffraction method. However, reducing the beam diameter to a small value and obtaining a thin parallel beam bundle are mutually contradictory requirements, and it is extremely difficult to obtain an electron optical system that can satisfy both at the same time. The reason for the difficulty is that in order to obtain a beam with a small diameter and close to parallel, a thin electron beam is converged with a point at a long distance from the lens as a convergence point. Since the point where the line intersects the lens optical axis is greatly deviated from a predetermined beam convergence point even by a slight aberration of the lens, the influence of the lens aberration appears more strongly than when the electron beam is converged near the lens (large convergence angle). That is because
このため収束レンズの収差を少なくして、平行にきわ
めて近く、しかも任意に微小な径の電子ビームが得られ
れば理想であるが、そのようなことはレンズの収差の影
響だけでなく、電子の波動としての性質からも限度のあ
る所で、高い位置分解能を得るため電子ビームを極力微
小径に絞る必要があるときは収束角は或る程度大きくし
なければならない。従って本発明の目的は、測定の目的
に応じて平行に近い微小径電子ビームと高位置分解能を
得るための極微小径ビームとが任意に可変選択できる電
子光学系を得ることである。Therefore, it would be ideal if the aberration of the converging lens could be reduced and an electron beam very close to parallel and arbitrarily small in diameter could be obtained. Where there is a limit due to the nature of the waves, when it is necessary to narrow the electron beam to a very small diameter in order to obtain a high positional resolution, the convergence angle must be increased to some extent. Accordingly, it is an object of the present invention to provide an electron optical system which can arbitrarily select a small-diameter electron beam close to parallel and a very small-diameter beam for obtaining high positional resolution according to the purpose of measurement.
（課題を解決するための手段） フィラメントから放射される電子をコンデンサレンズ
で収束させ、この収束された電子ビームの径を絞りで制
限し、この制限された電子ビームを、磁場の強さの変化
が弱い側を上記コンデンサレンズ側に向け、磁場の強さ
の変化が弱い側を試料側に向けた非対称磁場を発生する
非対称対物レンズで試料面上に収束させると共に、この
レンズの光源側の電子線収束点から同レンズ中心までの
距離より、同レンズ中心から試料側の電子線収束点まで
の距離を長くするようにした。(Means for Solving the Problems) Electrons radiated from the filament are converged by a condenser lens, the diameter of the converged electron beam is limited by a diaphragm, and the restricted electron beam is subjected to a change in the strength of a magnetic field. Is focused on the sample surface with an asymmetric objective lens that generates an asymmetric magnetic field with the weak side facing the condenser lens and the side with the weaker change in magnetic field strength facing the sample side, and the electron on the light source side of this lens. The distance from the center of the lens to the electron beam convergence point on the sample side was made longer than the distance from the line convergence point to the center of the lens.
更に、上記対物レンズとコンデンサレンズの間に第２
の対物レンズを配置し、コンデンサレンズで収束された
電子ビームを第２対物レンズと上記非対称レンズとの間
で一旦収束させるようにした。Further, a second lens is provided between the objective lens and the condenser lens.
Is arranged, and the electron beam converged by the condenser lens is once converged between the second objective lens and the asymmetric lens.
（作用） 平行に近いビームを得る為には、対物レンズとして長
焦点レンズを使用しなければならない。その対物レンズ
を用いて拡大系とするとかなり平行性の良いビームが得
られる。しかし、長焦点レンズを通常の対称磁場レンズ
で作ると球面収差係数が極端に大きくなってしまう。そ
こで極度の非対称磁場レンズを用いると、比較的、球面
収差係数を小さくすることができる。従って微小径で平
行に近い電子ビームが得られる。(Operation) In order to obtain a nearly parallel beam, a long focal length lens must be used as an objective lens. If the objective lens is used as a magnifying system, a beam with excellent parallelism can be obtained. However, when the long focal length lens is formed by a normal symmetric magnetic field lens, the spherical aberration coefficient becomes extremely large. Therefore, if an extremely asymmetric magnetic field lens is used, the spherical aberration coefficient can be relatively reduced. Therefore, an electron beam having a very small diameter and nearly parallel is obtained.
上述構成によると、電子ビームのビーム径，収束角は
固定したものとなる。上記非対称物レンズとコンデンサ
レンズとの間に第２の対物レンズを挿入することによ
り、非対称対物レンズの電子ビーム入射側の空間におけ
る電子ビームの収束点の位置を変えることができ、それ
によって試料面に収束する電子ビームのビーム径および
収束角を色々に変えることが可能となる。According to the above configuration, the beam diameter and the convergence angle of the electron beam are fixed. By inserting the second objective lens between the asymmetric object lens and the condenser lens, it is possible to change the position of the convergence point of the electron beam in the space on the electron beam incident side of the asymmetric objective lens. It is possible to change the beam diameter and the convergence angle of the electron beam converging in various ways.
（実施例） 第１図は対物レンズが一段である従来例を説明する図
である。１はフィラメント、２は絞りで、３は第１コン
デンサレンズ、４は第２コンデンサレンズで、フィラメ
ント１から放射され、絞り２で径が制限された電子ビー
ムを第1,第２のコンデンサレンズで２段に縮小して収束
させる。このようにして収束された電子ビームを絞り５
によって再びビーム径を制限して非対称対物レンズ６に
入射させ、非対称対物レンズ６により試料Ｓ上に収束さ
せる。第２コンデンサレンズの電子ビーム収束点と試料
Ｓ上の収束点とは対物レンズ６の共役点で、コンデンサ
レンズ４の収束点の方が試料よりも対物レンズ６に近
い。非対称対物レンズ６は磁場強度の変化の大きい側を
コンデンサレンズ４に向けている。この構成により、収
束角約１×10-3ラジアン、ビーム径0.1μｍの電子ビー
ムが得られる。対物レンズ６と試料Ｓとの間に走査コイ
ル７が配置されて、電子ビームによる試料面の走査が可
能である。(Example) FIG. 1 is a view for explaining a conventional example in which an objective lens has one stage. 1 is a filament, 2 is an aperture, 3 is a first condenser lens, 4 is a second condenser lens, and an electron beam radiated from the filament 1 and having a diameter restricted by the aperture 2 is passed through the first and second condenser lenses. It is reduced to two stages and converged. The electron beam converged in this manner is focused on the aperture 5.
Then, the beam diameter is again limited and the beam is made incident on the asymmetric objective lens 6 and converged on the sample S by the asymmetric objective lens 6. The convergence point of the electron beam of the second condenser lens and the convergence point on the sample S are conjugate points of the objective lens 6, and the convergence point of the condenser lens 4 is closer to the objective lens 6 than the specimen. The asymmetric objective lens 6 faces the condenser lens 4 on the side where the change in the magnetic field strength is large. With this configuration, an electron beam having a convergence angle of about 1 × 10 −3 radians and a beam diameter of 0.1 μm can be obtained. A scanning coil 7 is arranged between the objective lens 6 and the sample S, so that the sample surface can be scanned by an electron beam.
第２図は本発明の一実施例を示す第１図の各部と対応
する部分には同じ符号を付し、一々の説明は省略する。
この発明の特徴は第２コンデンサレンズ４と非対称対物
レンズ６との間に第２の対物レンズ８を配置した点にあ
る。この電子光学系では非対称対物レンズ６と第２対物
レンズ８の収束力が夫々可変である。第２対物レンズ８
の収束力を強くしてビーム収束点を自身に近づけ、非対
称対物レンズ６の収束力を弱めてビームを試料Ｓ上に収
束させるようにすると、試料面でのビーム収束角は大に
なる。逆にするとビームは平行ビームに近くなる。ビー
ムを平行ビームに最も近づけたときの試料面での収束角
は約１×10-3ラジアンである。今概算的にビーム収束径
を求めてみると、電子線波長を１Åとして、1000Å幅の
スリットを通過した電子線束の広がり角が１×10-3ラジ
アンであるから、収束角が１×10-3ラジアンである電子
ビームの収束径も1000Å＝0.1μｍ程度が限度である。
これより一桁収束径を小さくするにはビーム収束角は１
×10-2ラジアル以上とする必要がある。この発明によれ
ば電子ビームの収束角を最小値から或る範囲で大きい側
へ可変であり、それに伴って位置分解能を上げることが
できる。従って微小径の平行電子ビームを必要とする微
小領域の電子回折測定や、高分解能の試料表面形状映像
を得る走査型電子顕微鏡による試料観察が一つの電子光
学系で単なる切換え操作だけで可能になる。In FIG. 2, parts corresponding to the respective parts in FIG. 1 showing one embodiment of the present invention are denoted by the same reference numerals, and each description is omitted.
A feature of the present invention is that a second objective lens 8 is arranged between the second condenser lens 4 and the asymmetric objective lens 6. In this electron optical system, the convergence of the asymmetric objective lens 6 and the second objective lens 8 is variable. Second objective lens 8
If the beam convergence point is made closer to itself and the beam convergence angle is made closer to itself, and the beam is focused on the sample S by weakening the convergence power of the asymmetric objective lens 6, the beam convergence angle on the sample surface becomes large. Conversely, the beam will be closer to a parallel beam. The convergence angle on the sample surface when the beam is closest to the parallel beam is about 1 × 10 -3 radians. Looking now estimated to determine the beam converging diameter, the electron beam wavelength as 1 Å, since the divergence angle of the electron beam flux passing through the slit of 1000Å width is 1 × 10 -3 radians, convergence angle 1 × 10 - The convergence diameter of an electron beam of 3 radians is limited to about 1000 ° = 0.1 μm.
To make the convergence diameter smaller by one digit, the beam convergence angle is 1
X10 -2 Radial or more. According to the present invention, the convergence angle of the electron beam can be changed from the minimum value to a larger value within a certain range, and the positional resolution can be increased accordingly. Therefore, electron diffraction measurement of a small area that requires a parallel electron beam with a small diameter, and sample observation with a scanning electron microscope that obtains a high-resolution image of the sample surface shape can be performed by a simple switching operation with one electron optical system. .
（発明の効果） 微小径の電子線平行ビームを得る方法として対物レン
ズの入射側焦点位置に収束する電子ビームを対物レンズ
で平行にし、対物レンズの出射側に所定の微小径例えば
0.1μｍのピンホールを置くと云う方法が考えられる
が、そのような微小径のピンホールは工作も困難な上、
得られるビームは甚だ暗いものとなり、回折によるビー
ムの広がりが無視できなくて、実際上平行線束は得られ
ない。本発明は非対称対物レンズを用い、対物レンズか
ら離れた所に電子ビームを収束させることでレンズの収
差を減らすことができたので、理論的限界に近い微小径
で収束角の小さな疑似平行微小径電子ビームを得ること
ができ、太い平行ビームからピンホールで微小径ビーム
を取出すような方法に比し、大へん明るい電子ビームを
得ることができる。また対物レンズを二段にし、相互の
収束力の大小を調節することで、ビームの収束角，ビー
ム径を可変とすることにより、微小径疑似平行ビームか
ら、やゝ収束角の大きい極微小収束径のビームまで任意
に選択可能となり、目的に応じて電子ビームの性質を適
当に選べるようになり、一つの電子光学系で多様な測定
方法が実施できることになる。(Effect of the Invention) As a method of obtaining a parallel beam of an electron beam having a small diameter, an electron beam converging at a focal position on the incident side of the objective lens is made parallel by the objective lens, and a predetermined minute diameter,
A method of placing a 0.1 μm pinhole is conceivable, but such a small diameter pinhole is difficult to machine, and
The resulting beam is very dark, and the spread of the beam due to diffraction cannot be neglected, and practically no parallel flux can be obtained. Since the present invention uses an asymmetric objective lens and converges the electron beam away from the objective lens to reduce lens aberrations, a quasi-parallel micro diameter with a small diameter close to the theoretical limit and a small convergence angle An electron beam can be obtained, and a very bright electron beam can be obtained as compared with a method of extracting a small-diameter beam from a thick parallel beam with a pinhole. In addition, by making the objective lens two-stage and adjusting the magnitude of the mutual convergence, the beam convergence angle and beam diameter are made variable, so that a very small convergence angle with a large ゝ convergence angle can be obtained from a small diameter pseudo-parallel beam. The diameter of the beam can be arbitrarily selected, the properties of the electron beam can be appropriately selected according to the purpose, and various measurement methods can be performed with one electron optical system.
第１図は対物レンズが一段である従来例の側面図、第２
図は本発明の一実施例の側面図である。 １……フィラメント、２……絞り、３……第１コンデン
サレンズ、４……第２コンデンサレンズ、５……絞り、
６……非対称対物レンズ、７……走査コイル、８……第
２対物レンズ、Ｓ……試料。FIG. 1 is a side view of a conventional example having a single objective lens, and FIG.
The figure is a side view of one embodiment of the present invention. 1 ... filament, 2 ... stop, 3 ... first condenser lens, 4 ... second condenser lens, 5 ... stop,
6 ... Asymmetrical objective lens, 7 ... Scan coil, 8 ... Second objective lens, S ... Sample.
Claims (1)
の径を絞りで制限し、その制限された電子ビームを第一
の対物レンズで収束させ、収束された電子ビームを、磁
場強度のレンズ光軸方向の変化率が上記第一の対物レン
ズ側の方が試料側よりも小であるような光軸方向に非対
称磁場分布を持った第二の対物レンズにより、試料側で
上記第一の対物レンズによる電子ビーム収束点から上記
第二の対物レンズ中心までの距離より遠い位置に収束さ
せるようにし、上記第一、第二の二つの対物レンズの強
度を調節可能としたことを特徴とする疑似平行微小径電
子線ビームを得る電子光学装置。The diameter of an electron beam converged by a condenser lens is limited by a stop, the converged electron beam is converged by a first objective lens, and the converged electron beam is converted into a lens optical axis having a magnetic field intensity. The second objective lens having an asymmetric magnetic field distribution in the optical axis direction such that the rate of change in direction is smaller on the first objective lens side than on the sample side, so that the first objective lens on the sample side A convergence point from the electron beam convergence point to a position farther than the distance from the center of the second objective lens, and the intensity of the first and second two objective lenses can be adjusted. An electron optical device that obtains a small-diameter electron beam.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP1037138A JP2619048B2 (en) | 1989-02-16 | 1989-02-16 | Electron optical device for obtaining quasi-parallel minute electron beam |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP1037138A JP2619048B2 (en) | 1989-02-16 | 1989-02-16 | Electron optical device for obtaining quasi-parallel minute electron beam |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH02216745A JPH02216745A (en) | 1990-08-29 |
| JP2619048B2 true JP2619048B2 (en) | 1997-06-11 |
Family
ID=12489259
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP1037138A Expired - Fee Related JP2619048B2 (en) | 1989-02-16 | 1989-02-16 | Electron optical device for obtaining quasi-parallel minute electron beam |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2619048B2 (en) |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5845782B2 (en) * | 1978-03-16 | 1983-10-12 | 日本電子株式会社 | Objective lenses for scanning electron microscopes, etc. |
-
1989
- 1989-02-16 JP JP1037138A patent/JP2619048B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH02216745A (en) | 1990-08-29 |
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